The present invention relates to a timing recovery device and a demodulator and, more particularly, to a timing recovery device and a demodulator suitable for use in a broadband digital radio communication system in which a burst signal begins with a preamble.
For a timing recovery device of a demodulator for a conventional broadband digital radio communication system which employs a preamble signal, there are described two schemes, for example, in literature xe2x80x9cCarrier-Clock Simultaneous Recovery Schemexe2x80x9d by Nagura, Matsumoto, Kubota and Kato, The Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE, RCS94-60, pp. 7-12, September 1994.
The one scheme is to estimate a timing phase from a preamble signal now widely used for OQPSK modulation. This preamble signal is a signal (of a xe2x80x9c1101xe2x80x9d pattern, for instance) which effects an alternate transition between two adjacent Nyquist points in a complex plane upon each occurrence of a symbol. A patent for this scheme is xe2x80x9cBurst Signal Demodulation Circuitxe2x80x9d (Pat. Appln. Laid-Open No. 35956/95, Inventors: Matsumoto and Kato).
The other scheme is to estimate a timing phase from a preamble signal widely used for QPSK modulation. This preamble signal is a xe2x80x9c0xcfx80xe2x80x9d modulation signal (of a xe2x80x9c1001xe2x80x9d pattern, for instance) which effects an alternate transition between two origin-symmetric Nyquist points in a complex plane upon each occurrence of a symbol. A patent for this scheme is xe2x80x9cBurst Signal Demodulation Circuitxe2x80x9d (Pat. Appln. Laid-Open No. 46658/96, Inventors: Nagura, Matsumoto and Kato).
According to these schemes, both of which utilize the fact that either preamble signal has a frequency component xc2xd that of a symbol frequency (fs), the receiver side calculates the correlation between the preamble signal and a xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t] output from a VCO, and estimates the timing phase from a vector angle indicated by the correlation value.
In either scheme the data sampling rate is only 2 [sample/symbol]; since this sampling rate is xc2xd the minimum value of the sampling rate (=4 [sample/symbol] needed in a conventional scheme which estimates the timing phase from the correlation between a nonlinearly processed signal (for example, an envelope) and a symbol frequency component exp[xe2x88x92j2xcfx80(fs)t] as described in, for example, literature xe2x80x9cSignal Detecting System and Burst Demodulating Equipmentxe2x80x9d (Pat. Appln. Laid-Open No. 141048/94, Inventor: Yoshida), the reduction of the sampling rate permits reduction of the power consumption of the receiver. The above-mentioned two schemes (Pat. Appln. Laid-Open No. 235956/95 and Pat. Appln. Laid-Open No. 46658/96) will be described below in detail.
A description will be given first of a timing recovery scheme (pat. Appln. Laid-Open 235956/95) that uses the preamble (xe2x80x9c1101xe2x80x9d pattern) signal which effects an alternate transition between two adjacent Nyquist points in a complex plane upon each occurrence of a symbol.
FIG. 17 is a block diagram depicting the above-mentioned demodulator containing a timing recovery device. In FIG. 17, reference numeral 100 denotes an antenna, 200 frequency converting means, 301 and 302 A/D converters, 400 a timing recovery device, and 500 data decision means; and in the timing recovery device 400, reference numeral 401 denotes one-symbol delay means, 402 conjugate complex multiplying means, 403 timing phase difference calculating means, and 404 a VCO.
Next, the operation of the conventional demodulator will be described. The antenna 100 receives an RF band preamble signal, and the frequency converting means 200 frequency-converts the RF band preamble signal to a base band preamble signal.
FIG. 18 is a signal space diagram of the base band preamble signal (xe2x80x9c1101xe2x80x9d pattern. In FIG. 18, reference character xcex8c denotes the carrier phase of the received signal; the preamble signal effects an alternate transition between Nyquist points xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d in the figure upon each occurrence of a symbol. The vector angle of the Nyquist point xe2x80x9cAxe2x80x9d is (xcex8cxe2x88x9245) (deg), and the vector angle of the Nyquist point xe2x80x9cBxe2x80x9d is (xcex8c+45) [deg]; the difference between the vector angles of the Nyquist points xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d is 90 [deg].
The A/D converter 301 samples an in-phase component of the base band preamble signal at a time t=xcfx84+iT/2 (where I=1,2,3, . . . , xcfx84 is a timing error (xe2x88x92T/2xe2x89xa6xcfx84 less than T/2) and T is a symbol period), and outputs a sampled preamble data sequence Ipi (where i=1,2,3, . . . ). Similarly, the A/D converter 302 samples a quadrature component of the base band preamble signal at a time t=xcfx84+iT/2, and outputs a samples preamble data sequence Qpi (where 1=1,2,3, . . . ).
Therefore, it is apparent that the sampling rate is 2[sample/symbol]. The sampling is performed by the leading edge of a recovered sample clock output from the timing recovery device 400 of the following stage, and during a timing phase estimating operation no phase control of the recovered sample clock is effected.
The timing recovery device 400 uses the preamble data sequence Ipi (where i=1,2,3, . . . ) and the preamble data sequence Qpi (where i=1,2,3, . . . ) to calculate the timing error xcfx84, and exercises phase control of the recovered sample clock and a recovered symbol clock to cancel the timing error xcfx84.
The recovered symbol clock mentioned herein is a clock of the symbol period obtained by frequency dividing the recovered sample clock down to xc2xd.
The data decision means 500 latches, by the recovered symbol clock, data at the Nyquist points from significant random data sequences Idi and Qdi (where i=1,2,3, . . . ) following the preamble after cancellation of the timing error xcfx84 by the timing recovery device 400. And the data decision means uses the latched Nyquist point data to decide data, and outputs demodulated data.
Next, the operation of the timing recovery device 400 will be described. The one-symbol delay means 401 delays the preamble data sequence Ipi (where i=1,2,3, . . . ) and the preamble data Qpi (where i=1,2,3, . . . ) by a one-symbol time interval, and the conjugate complex multiplying means 402 performs conjugate complex multiplications of the preamble data sequences (Ipi, Qpi) and one-symbol old preamble data sequences (Ipixe2x88x922, Qpixe2x88x922) by the following equations.
Idi=(Ipixc3x97Ipixe2x88x922)+(Qpixc3x97Qpixe2x88x922)xe2x80x83xe2x80x83(1a)
Qdi=(Qpixc3x97Ipixe2x88x922)+(Ipixc3x97PQixe2x88x922)xe2x80x83xe2x80x83(1b)
By this processing, the preamble signal is differential-detected. With such processing, it is possible to obtain a preamble signal which effects an alternate transition between points xe2x80x9cCxe2x80x9d and xe2x80x9cDxe2x80x9d upon each occurrence of a symbol independently of the carrier phase xcex8c as depicted in FIG. 19. The phase xcex8x(t) indicated by this preamble signal has a xc2xd symbol frequency component since it makes a phase transition from +90 [deg] to xe2x88x9290 [deg] and a phase transition from xe2x88x9290 [deg] to +90 [deg] alternately with one symbol period as depicted in FIG. 20.
Then, the timing phase difference calculating means 403 calculates the correlation between the phase xcex8x(t) and the xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t] output from the VCO. Concretely, letting the phases of the signals (IDi, QDi) be represented by xcex8xi, the timing phase difference calculating means performs the following multiplications
MIi=xcex8Xixc3x97cos xcfx80i/2xe2x80x83xe2x80x83(2a)
MQi=xcex8Xixc3x97sin xcfx80i/2xe2x80x83xe2x80x83(2b)
The timing phase difference calculating means averages the multiplied results (MIi, MQi), and outputs a correlation value (xcexa3MI, xcexa3MQ). Incidentally, since in the multiplications of Equations (2a) and (2b) cos xcfx80i/2=1,0,xe2x88x921,0, . . . and sin xcfx80i/2=0,1,0,xe2x88x921, . . . , the above-said correlation values (xcexa3MI, xcexa3MQ) can easily be obtained. For example, in the case of averaging the multiplied values over four symbols, the correlation value (xcexa3MI, xcexa3MQ) can be obtained by the following equations.
xcexa3MI=(xcex8Xixe2x88x92xcex8Xi+4+xcex8Xi+4xe2x88x92xcex8Xi+6+xcex8Xi+8xe2x88x92xcex8Xi+10+xcex8Xi+12xe2x88x92xcex8Xi+14)/8xe2x80x83xe2x80x83(3a)
xcexa3MQ=(xcex8Xi+1xe2x88x92xcex8Xi+3+xcex8Xi+5xe2x88x92xcex8Xi+76+xcex8Xi+9xe2x88x92xcex8Xi+11+xcex8Xi+13xe2x88x92xcex8Xi+15)/8xe2x80x83xe2x80x83(3b)
The vector angle that this correlation value indicates
xe2x80x83QT=tanxe2x88x921(xcexa3MQ/xcexa3MI)
is a timing phase difference when normalized with two symbol periods (2T), and hence the timing phase difference xcex8s [deg] when normalized with the symbol period (T) is obtained by the following equation.
xcex8s=2xcex8Tmod360xe2x80x83xe2x80x83(4)
The relationship between the timing phase difference xcex8s and the timing error xcfx84 is as follows:
In the case of xcex8s greater than 180 [deg],
xcfx84=(xcex8sxe2x88x92360)T/360xe2x80x83xe2x80x83(5a)
In the case of xcex8xe2x89xa6180 [deg]
xcfx84=(xcex8s)T/360xe2x80x83xe2x80x83(5b)
For example, in the case where the phase signal xcex8X(t) is sampled at the timing shown in FIG. 20 to obtain a data sequence {xcex8Xi, xcex8Xi+1, xcex8Xi+2, xcex8Xi+3, . . . }, such a correlation value (xcexa3MI, xcexa3MQ) and a timing phase difference xcex8T as shown in FIG. 21 are obtained.
Based on the timing error xcfx84 obtained by the above calculation, the timing phase difference calculating means 403 supplies the VCO 404 of the following stage with a control signal that cancels the timing errorxcfx84. The VCO 404 responds to the control signal from the timing phase difference calculating means to control the phases of the recovered sample clock and the recovered symbol clock, reducing the timing errors down to xe2x80x9c0xe2x80x9d.
Next, a description will be given of the timing recovery scheme (Pat. Appln. Laid-Open No. 46658/96) which uses the preamble (xe2x80x9c0xcfx80xe2x80x9d modulation signal of axe2x80x9c1001xe2x80x9d pattern, for instance) signal which makes an alternate transition between two origin-symmetric Nyquist points in a complex plane upon each occurrence of a symbol.
In FIG. 22 wherein the parts corresponding to those in FIG. 17 are identified by the same reference numerals, there is depicted demodulating equipment containing the above-mentioned timing recovery device. In FIG. 22, reference numerals 400a denotes a timing recovery device, 403a timing phase difference calculating means, 405a I-channel correlation calculating means, 405b Q-channel correlation calculating means, and 406 vector combining/selecting means.
FIG. 23 is a block diagram of the vector combining/selecting means 406, in which reference numeral 407a denotes first vector combining means, 407b second vector combining means, 407c third vector combining means, 407d fourth vector combining means, 408 maximum absolute value detecting means, and 409 selecting means.
In FIG. 24 wherein the parts corresponding to those in FIG. 23 are identified by the same reference numerals, there is shown another block diagram of the vector combining/selecting means 406, in which reference numerals 410a and 410b denote adding means, 411a first selecting means, 411b second selecting means, 411c third selecting means, and 411d fourth selecting means.
Next, the operation of the demodulator will be described. As is the case with the configuration of the afore-described FIG. 17 prior art example, the antenna 100 receives the RF band preamble signal, and the frequency converting means 200 frequency converts the RF band preamble signal to the base band preamble signal.
In FIG. 25 there is depicted a signal space diagram of the base band preamble signal (of the xe2x80x9c1001xe2x80x9d pattern). In FIG. 25, reference character xcex8c denotes the carrier phase of the received signal, and the preamble signal performs an alternate transition between the Nyquist points xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d through the origin for each symbol.
The vector angle of the Nyquist point xe2x80x9cAxe2x80x9d is xcex8c [deg], the vector angle of the Nyquist point xe2x80x9cBxe2x80x9d is (xcex8c+180) [deg], and the difference between the vector angles of the Nyquist points xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d is 180 [deg].
As in the prior art example of FIG. 17, the A/D converter 301 samples the in-phase component of the base band preamble signal at time t=xcfx84+iT/2 (where I=1,2,3, . . . , xcfx84 is a timing error (xe2x88x92T/2xe2x89xa6xcfx84 less than T/2), and T is the symbol period), and outputs the sampled preamble data sequence Ipi (where i=1,2,3, . . . ). 
Similarly, the A/D converter 302 samples the quadrature component of the base band preamble signal at time t=xcfx84+iT, and outputs the sampled preamble data sequence Qpi (where i=1,2,3, . . . ). The timing recovery device 400a does not effect phase control of the recovered sample clock during the timing phase estimating operation.
The timing recovery device 400a, as in the prior art example of FIG. 17, uses the preamble data sequence Ipi (where i=1,2,3, . . . ) and the preamble data sequence Qpi (where i=1,2,3, . . . ) to calculate the timing error xcfx84, and exercises phase control of the recovered sample clock and the recovered symbol clock to cancel the timing error xcfx84. The recovered symbol clock is a clock of the symbol period obtained by frequency dividing the recovered sample clock down to xc2xd.
The data decision means 500 latches, by the recovered symbol clock as in the prior art example of FIG. 17, data at the Nyquist points from the significant random data sequences Idi and Qdi (where i=1,2,3, . . . ) following the preamble after cancellation of the timing error xcfx84 by the timing recovery device 400. And the data decision means uses the latched Nyquist point data to decide data, and outputs demodulated data.
Next, the operation of the timing recovery device 400a will be described. In the case of receiving the preamble signal which performs an alternate transition between the origin-symmetric two Nyquist points for each symbol as depicted in FIG. 25, the prior art example of FIG. 17 cannot be used for the reasons given below. When the preamble signal is differential-detected, the phase signal xcex8X(t) (of the output from the conjugate complex multiplying means) after the differential detection is always about 180 [deg], and does not provide the frequency component xc2xd the symbol frequency, and consequently the correlation between this phase signal and the xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t] goes to xe2x80x9c0xe2x80x9d.
Hence, the prior art example of FIG. 22 calculates the correlation between each of the in-phase component I(t) and quadrature component Q(t) of the preamble signal of FIG. 25 and the xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t]. Concretely, the I-channel correlation calculating means 405a performs the following multiplications of an oversampled preamble data sequence Ipi (where i=1,2,3, . . . )
Ici=Ipixc3x97cos xcfx80i/2xe2x80x83xe2x80x83(6a)
Isi=Ipixc3x97sin xcfx80i/2xe2x80x83xe2x80x83(6b)
The I-channel correlation calculating means averages the multiplication results (Ici, Isi) to obtain a correlation value (CI, SI). The Q-channel collation calculating means 405b performs the following multiplications of an oversampled preamble data sequence Qpi (where i=1,2,3, . . . )
Qci=Qpixc3x97cos xcfx80i/2xe2x80x83xe2x80x83(7a)
Qsi=Qpixc3x97sin xcfx80i/2xe2x80x83xe2x80x83(7b)
The Q-channel correlation calculating means averages the multiplication results (Qci, Qsi) to obtain the correlation value (CQ, SQ).
Incidentally, since in the multiplications of Equations (6a), (6b), (7a) and (7b) cos xcfx80i/2=1, 0, xe2x88x921, 0, . . . , and sin xcfx80i/2=0, 1, 0, xe2x88x921, . . . , the above correlation values (CI, SI) and (CQ, CI) can easily be obtained. For instance, in the case of the averaging the multiplied results over four symbols, the correlation value (CI, SI) can be obtained by the following equations:
CI=(Ipixe2x88x92Ipi+2+Ipi+4xe2x88x92Ipi+6+Ipi+8xe2x88x92Ipi+10+Ipi+12xe2x88x92Ipi+14)/8xe2x80x83xe2x80x83(8a)
SI=(Ipi+1xe2x88x92Ipi+3+Ipi+5xe2x88x92Ipi+7+Ipi+9xe2x88x92Ipi+11+Ipi+13xe2x88x92Ipi+15)/8xe2x80x83xe2x80x83(8b)
The correlation value (CQ, SQ) can be obtained by the following equations:
CQ=(Qpixe2x88x92Qpi+2+Qpi+4xe2x88x92Qpi+6+Qpi+8xe2x88x92Qpi+10+Qpi+12xe2x88x92Qpi+14)/8xe2x80x83xe2x80x83(9a)
SQ=(Qpi+1xe2x88x92Qpi+3+Qpi+5xe2x88x92Qpi+7+Qpi+9xe2x88x92Qpi+11+Qpi+13xe2x88x92Qpi+15)/8xe2x80x83xe2x80x83(9b)
The vector angles that the correlation values (CI, CQ) and (SI, SQ) represent both indicate timing phase errors as in the prior art example of FIG. 17, but according to.the carrier phase xcex8c, the angles of the correlation vectors may sometimes face in the same or opposite directions or either one of them may disappear.
For example, when a preamble signal whose carrier phase xcex8c is in the range of (90 less than xcex8c less than 180) or (270 less than xcex8c less than 360) as shown in FIG. 25 is sampled at the timing shown in FIGS. 26 and 27 to obtain a data sequence {Ipi, Ipi+1, IPi+2, Ipi+3, . . . } and a data sequence {Qpi, Qpi+1, Qpi+2, Qpi+3, . . . }, such correlation values (CI, SI) and (CQ, SQ) as depicted in FIG. 28 are obtained, and the angles of the correlation vectors face in opposite directions.
On the other hand, when a preamble signal whose phase xcex8c is in the range of (0 less than xcex8c less than 90) or (180 less than xcex8c less than 270) as shown in FIG. 29 is sampled at the timing shown in FIGS. 30 and 31 to obtain a data sequence {Ipi, Ipi+1, Ipi+2, Ipi+3, . . . } and a data sequence {Qpi, Qpi+1, Qpi+2, Qpi+3, . . . }, such correlation values (CI, SI) and (CQ, SQ) as depicted in FIG. 32 are obtained, and the angles of the correlation vectors face in the same direction. Further, it is also evident that each vector length varies with the carrier phase xcex8c; when xcex8c={0, 180}, the vector of the correlation value disappears, and when xcex8c={90, xe2x88x9290}, the vector of the correlation value (CQ, SQ).
In view of the above, to exclude the influence of the carrier phase xcex8c, the vector combining/selecting means 406 combines the correlation values (CI, CQ) and (SI, SQ) into the four states described later on, and selects the combined vector of the highest SN ratio, and the timing phase difference calculating means 403a calculates the timing phase from the combined vector selected by the vector combining/selecting means 406. In the vector combining/selecting means 406 of FIG. 23 the maximum absolute value detecting means 408 calculates four absolute values of CI, CQ, SI and SQ, and detects which of the four absolute values is maximum among them. The first vector combing means 407a outputs a combined vector (G1C, G1S) by the following equations:
G1C=CI+sign[CI]xc2x7|CQ|xe2x80x83xe2x80x83(10a)
G1S=SI+sign[CIxc2x7CQ]xc2x7|SQ|xe2x80x83xe2x80x83(10b)
The second vector combining means 407b outputs a combined vector (G2C, G2S) by the following equations:
G2C=CQ+sign[CQ]xc2x7|CI|xe2x80x83xe2x80x83(11a)
G2S=SQ+sign[CIxc2x7CQ]xc2x7|SI|xe2x80x83xe2x80x83(11b)
The third vector combining means 407c outputs a combined vector (G3C, G3S) by the following equations:
G3C=CI+sign[SIxc2x7SQ]xc2x7|CQ|xe2x80x83xe2x80x83(12a)
G3S=SI+sign[SI]xc2x7|SQ|xe2x80x83xe2x80x83(12b)
The fourth vector combining means 407d outputs a combined vector (G4C, G4S) by the following equations:
G4C=CQ+sign[SIxc2x7SQ]xc2x7|CI|xe2x80x83xe2x80x83(13a)
G4S=SQ+sign[SQ]xc2x7|SI|xe2x80x83xe2x80x83(13b)
In the above, sign[*] means the sign (xcx9cxc2x11)) in [ ].
The selecting means 409 receives the detected signal from the maximum absolute value detecting means 408, and selects the combined correlation value (xcexa3C, xcexa3S) from among (G1C, G1S), (G2C, G2S), (G3C, G3S) and (G4C, G4S).
(xcexa3C, xcexa3S)=(G1C, G1S) (when |CI| is maximum)xe2x80x83xe2x80x83(14a)
(xcexa3C, xcexa3S)=(G2C, G2S) (when |CQ| is maximum)xe2x80x83xe2x80x83(14b)
(xcexa3C, xcexa3S)=(G3C, G3S) (when |SI| is maximum)xe2x80x83xe2x80x83(14c)
(xcexa3C, xcexa3S)=(G4C, G4S) (when |SQ| is maximum)xe2x80x83xe2x80x83(14d)
By such processing the influence of the carrier phase xcex8c is excluded, and a combined vector in which the vectors of the correlations (CI, CQ) and (SI, SQ) face in the same direction is selected as a vector that is the most suitable for the timing phase estimation. For example, in the case of FIG. 28, a combined vector is selected which is obtained by adding the correlation value (CI, SI) with the correlation value (CQ, SQ) of the smaller vector length reversed to face in the same direction as does the former. The resulting correlation value (xcexa3C, xcexa3S) is such as shown in FIG. 33. In the case of FIG. 32, a combined vector is selected which is obtained by adding the correlation value (CQ, SQ) of the smaller vector length intact to the correlation value (CI, SI). The resulting correlation value (xcexa3C, xcexa3S) is such as shown in FIG. 34.
Incidentally, the vector combining/selecting means 406 may be adapted not only to select one of the four combined vectors pre-generated from CI, SI, CQ and SQ as described above in respect of FIG. 23 but also to activate any one of the combining means 407a, 407b, 407c and 407d based on the detected result by the maximum absolute detecting means 408 as depicted in FIG. 24, and in the latter case, too, the same output results as in the former case could be obtained. As compared with the configuration of FIG. 23, the FIG. 24 configuration permits reduction of the scale of circuitry. In the vector combining/selecting means depicted in FIG. 24, selecting means 411a, 411b, 411c and 411d output the following values based on the detected results by the maximum absolute value detecting means 408.
The output SEL1 from the first selecting means 411a is:
SEL1=CI (when |CI| or |SI| is maximum)xe2x80x83xe2x80x83(15a)
SEL1=CQ (when |CQ| or |SQ| is maximum)xe2x80x83xe2x80x83(15b)
The output SEL2 from the second selecting means 411b is:
SEL2=sign[CI]xc2x7|CQ| (when |CI| is maximumxe2x80x83xe2x80x83(16a)
SEL2=sign[CQ]xc2x7|CI| (when |CQ| is maximumxe2x80x83xe2x80x83(16b)
SEL2=sign[SIxc2x7SQ]xc2x7|CQ| (when |SI| is maximumxe2x80x83xe2x80x83(16c)
SEL2=sign[SIxc2x7SQ]xc2x7|CI| (when |SQ| is maximumxe2x80x83xe2x80x83(16d)
The output SEL3 from the third selecting means 411c is:
xe2x80x83SEL3=sign[CIxc2x7CQ]xc2x7|SQ| (when |CI| is maximumxe2x80x83xe2x80x83(17a)
SEL3=sign[CIxc2x7CQ]xc2x7|SI| (when |CQ| is maximumxe2x80x83xe2x80x83(17b)
SEL3=sign[SI]xc2x7|SQ| (when |SI| is maximumxe2x80x83xe2x80x83(17c)
SEL3=sign[SQ]xc2x7|SI| (when |SQ| is maximumxe2x80x83xe2x80x83(17d)
The output SEL4 from the fourth selecting means 411d is:
SEL4=SI (when |CI| or |SI| is maximum)xe2x80x83xe2x80x83(18a)
SEL4=SQ (when |CQ| or |SQ| is maximum)xe2x80x83xe2x80x83(18b)
An adder 410a adds SEL1 and SEL2 together and outputs xcexa3C as the added result. An adder 410b adds SEL3 and SEL4 together and outputs xcexa3S as the added result.
By the above processing the vector combining/selecting means of the FIG. 24 construction outputs the same values as those provided by the vector combining/selecting means of the FIG. 23 construction.
Next, the timing phase difference calculating means 403a calculates the vector angle
xcex82s=tanxe2x88x921(xcexa3S/xcexa3C)xe2x80x83xe2x80x83(19)
that the composite correlation value (xcexa3C, xcexa3S) indicates. xcex82s is the timing phase angle when normalized by a two-symbol period (2T) as is the case with the aforementioned xcex8T, and accordingly, the timing phase difference xcex8s [deg] when normalized by the symbol period (T) is given by Equation (20).
xcex8s=2xcex82smod360xe2x80x83xe2x80x83(20)
xcex82s in the case of FIG. 33 and xcex82s in the case of FIG. 34 differ by 180 [deg], but by the processing of Equation (20), xcex8s derived from xcex82s in FIG. 33 and xcex8s derived from xcex82s in FIG. 34 match each other.
Incidentally, the relationship between the timing phase difference xcex8s and the timing error xcfx84 is such as indicated by Equations (5a) and (5b).
Based on the timing error xcfx84 obtained by the above operation, the timing phase difference calculating means 403a supplies the VCO 404 of the following stage with a control signal which cancels the timing errorxcfx84. Upon receiving the control signal from the timing phase difference calculating means, the VCO 404 controls the phases the recovered sample clock and the recovered symbol clock to reduce the timing errors down to xe2x80x9c0xe2x80x9d.
As described above, the two timing recovery devices 400 and 400a using the preamble in the prior art examples both calculate the correlation between the xc2xd symbol frequency component contained in the preamble signal and the xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t] output from the VCO, and estimate the timing phase from the vector angle indicated by the correlation value, and since the sampling rate is as low as 2 [sample/symbol], the conventional schemes are particularly effective in the broadband radio communication system, but either of them is provided with means for excluding the influence of the carrier phase differencexcex8c, which enlarges the scale of circuitry and increases the computational complexity.
For example, the timing recovery device 400 performs differential detection by the one-symbol delay means 401 and the conjugate complex multiplying means 402 to exclude the influence of the carrier phasexcex8c. To this end, the conjugate complex multiplying means 402 requires four multipliers and two adders, and hence involves a large circuit scale and a large amount of operation.
The timing recovery device 400a performs complex add-subtract processing and select processing by the vector combining/selecting means 406 to exclude the influence of the carrier phase differencexcex8c. In the case of selecting one of the four combined vectors pre-generated from CI, SI, CQ and SQ, the vector combining/selecting means 406 requires a total of eight adders contained in the combining means 407a, 407b, 407c and 407d, and the selecting means 409 for selecting two data sequences from among eight data sequences.
Further, in the case of implementing the vector combining/selecting means 406 by the FIG. 24 configuration, since the number of adders can be decreased from eight to two, the circuit scale can be reduced as compared with the FIG. 23 configuration, but even this configuration requires the four selecting means 411a, 411b, 411c and 411d in the preceding stages of the adders 410a and 410b, and involves complicated processing.
Besides, the above-described timing recovery devices 400 and 400a are effective only in the case where the timing for receiving the preamble signal is known; for example, in the case where the timing for receiving a burst signal, which is generated at turn0on of a mobile terminal equipment or at its reconnection after return from shadowing, is unknown, the timing for receiving the preamble is not known, and hence the conventional timing recovery devices cannot be used.
The present invention has for its object to provide a timing recovery device that solves such problems as described above and permits reduction of the circuit scale and computational complexity, and a demodulator using the timing recovery device.
Another object of the present invention is to provide a timing recovery device effective for either of a signal (for example,xe2x80x9c1101xe2x80x9d pattern) that performs an alternate transition between two adjacent Nyquist points in a complex plane upon each occurrence of a symbol and a xe2x80x9c0xcfx80xe2x80x9d modulation signal (for example, xe2x80x9c1001xe2x80x9d pattern) that performs an alternate transition between two origin-symmetric Nyquist points in the complex plane upon each occurrence of a symbol, and a demodulator using the timing recovery device.
Still another object of the present invention is to provide a timing recovery device that is effective even when the timing for receiving a preamble is not known, and a demodulator using the recovery device.
A timing recovery device according to an aspect of the present invention is characterized by the provision of: adding means for adding together an in-phase component of a base band signal and a quadrature component of the base band signal and for outputting a signal after the addition as an added signal; subtracting means for subtracting the in-phase component of the base band signal and the quadrature component of the base band signal from each other and for outputting a signal after the subtraction as a subtracted signal; added value correlation calculating means for calculating the correlation between said added signal and a xc2xd symbol frequency component generated at the receiver side, and for outputting the calculated correlation value as an added correlation signal; subtracted value correlation calculating means for calculating the correlation between said subtracted signal and said xc2xd symbol frequency component, and for outputting the calculated correlation value as a subtracted correlation signal; vector selecting means for comparing the magnitude of said added correlation signal and the magnitude of said subtracted correlation signal, for selecting the correlation signal of the larger magnitude, and for outputting the selected correlation signal as a selected correlation signal; and timing phase difference calculating means for calculating a timing phase difference through utilization of the vector angle indicated by said selected correlation signal.
According to another aspect of the invention, the timing recovery device is characterized in that said timing phase difference calculating means calculates the vector angle and the vector length indicated by said selected correlation signal, and when said vector length is large, decides that said preamble signal is detected, and calculates the timing phase difference through utilization of the vector angle indicated by said selected correlation signal at that time.
According to another aspect of the invention, the timing recovery device is characterized by further provision of recovered sample clock oscillating means for outputting a recovered sample clock for sampling said base band signal and a recovered xc2xd symbol frequency component, and for effecting phase control to reduce a timing error down to xe2x80x9c0xe2x80x9d through utilization of said timing phase difference information.
According to another aspect of the invention, the timing recovery device is characterized in that: said added value correlation calculating means, said subtracted value correlation calculating means, said vector selecting means, said timing phase difference calculating means and said recovered sample clock oscillating means use, for their processing, a base band signal sampled by said recovered sample clock; and said added value correlation calculating means and said subtracted value correlation calculating means render said xc2xd symbol frequency component to said recovered xc2xd symbol frequency component.
According to another aspect of the invention, the timing recovery device is characterized by further provision of: phase detecting means for detecting the timing phase through the use of said base band signal sampled by said recovered sample clock and for outputting the detected signal as a phase detected signal; and phase detected signal averaging means for averaging said phase detected signal and for outputting the average as a phase lead/lag signal; wherein said recovered sample clock oscillating means uses both of said timing phase difference information and said phase lead/lag signal to effect phase control to reduce the timing error down toxe2x80x9c0xe2x80x9d.
According to another aspect of the invention, the timing recovery device is characterized by further provision of asynchronous sample clock oscillating means for outputting an asynchronous sample clock for sampling said base band signal and an asynchronous xc2xd symbol frequency component.
According to another aspect of the invention, timing recovery device is characterized in that: said added value correlation calculating means, said subtracted value correlation calculating means, said vector selecting means, said timing phase difference calculating means and said asynchronous sample clock oscillating means use, for their processing, the base band signal sampled by said asynchronous sample clock; and the added value correlation calculating means; and said added value correlation calculating means and said subtracted value correlation calculating means render said xc2xd symbol frequency component to said asynchronous xc2xd symbol frequency component.
A timing recovery device according to another aspect of the invention is characterized by the provision of: adding means for adding together an in-phase component of a base band signal and a quadrature component of the base band signal and for outputting a signal after the addition as an added signal; subtracting means for subtracting the in-phase component of the base band signal and the quadrature component of the base band signal from each other and for outputting a signal after the subtraction as a subtracted signal; added value correlation calculating means for calculating the correlation between said added signal and a xc2xd symbol frequency component generated at the receiver side, and for outputting the calculated correlation value as an added correlation signal; subtracted value correlation calculating means for calculating the correlation between said subtracted signal and said xc2xd symbol frequency component, and for outputting the calculated correlation value as a subtracted correlation signal; vector selecting means for comparing the magnitude of said added correlation signal and the magnitude of said subtracted correlation signal, for selecting the correlation signal of the larger magnitude, and for outputting the selected correlation signal as a selected correlation signal; weighting means for weighting said selected correlation signal in accordance with the magnitude of the vector length indicated by said selected correlation signal, and for outputting said weighted selected correlation signal as a weighted correlation signal; weighted signalaveraging means for averaging said weighted correlation signal and for outputting the average as a weighted average correlation signal; and timing phase difference calculating means for calculating a timing phase difference through utilization of the vector angle indicated by said averaged correlation signal.
According to another aspect of the invention, the timing recovery device is characterized in that said timing phase difference calculating means calculates the vector angle and vector length indicated by said weighted average correlation signal, and when said vector length is large, detects that said preamble signal is detected, and calculates the timing difference through utilization of the vector angle indicated by said selected correlation signal at that time.
According to another aspect of the invention, the timing recovery device is characterized by further provision of recovered sample clock oscillating means for outputting a recovered sample clock for sampling said base band signal and a recovered xc2xd symbol frequency component, and for effecting phase control to reduce a timing error down to xe2x80x9c0xe2x80x9d through utilization of said timing phase difference information.
According to another aspect of the invention, the timing recovery device is characterized in that: said added value correlation calculating means, said subtracted value correlation calculating means, said vector selecting means, said weighting means, said weighted signal averaging means, said timing phase difference calculating means and said recovered sample clock oscillating means use, for their processing, a base band signal sampled by said recovered sample clock; and said added value correlation calculating means and said subtracted value correlation calculating means render said xc2xd symbol frequency component to said recovered xc2xd symbol frequency component.
According to another aspect of the invention, the timing recovery device is characterized in that: said weighted signal averaging means comprises a first low-pass filter of a small time constant and a second low-pass filter of a large time constant which are supplied with tsaid weighted correlation signal, and at the time of phase control, sets xe2x80x9c0xe2x80x9d in a quadrature component and (in-phase component2+quadrature component2)xc2xd prior to the phase control in an in-phase component in each of said first and second low-pass filters; said timing phase difference calculating means calculates a first vector angle and a first vector length indicated by said first low-pass filter, and when said vector length is large, decides that said preamble signal is detected, calculates an initial timing phase difference through the use of said first vector angle, calculates a second vector angle and a second vector length indicated by said second low-pass filter, and when said second vector length is large after said first phase control, periodically calculates a timing phase difference for phase following use through the use of said second vector angle; and said recovered sample clock oscillating means uses both of said initial timing phase difference and said phase-following timing phase difference as said timing phase difference information to effect phase control to reduce the timing error down to xe2x80x9c0xe2x80x9d.
According to another aspect of the invention, the timing recovery device is characterized by further provision of asynchronous sample clock oscillating means for outputting an asynchronous sample clock for sampling said base band signal and an asynchronous xc2xd symbol frequency component.
According to another aspect of the invention, the timing recovery device is characterized in that: said added value correlation calculating means, said subtracted value correlation calculating means, said vector selecting means, said weighting means, said weighted signal averaging means, said timing phase difference calculating means and said asynchronous sample clock oscillating means use, for their processing, a base band signal sampled by said asynchronous sample clock; and said added value correlation calculating means and said subtracted value correlation calculating means render said xc2xd symbol frequency component to said asynchronous xc2xd symbol frequency component.
According to another aspect of the invention, the timing recovery device is characterized in that: said weighted signal averaging means further comprises a first low-pass filter of a small time constant and a second low-pass filter of a large time constant which are supplied with said weighted correlation signal; and said timing phase difference calculating means calculates a first vector angle and a first vector length indicated by said first low-pass filter, and when said first vector length is large, decides that said preamble signal is detected, calculates an initial timing phase difference through the use of said first vector angle, calculates a second vector angle and a second vector length indicated by said second low-pass filter, and when said second vector length is large after said first phase control, periodically calculates a timing phase difference for phase following use through the use of said second vector angle.
A demodulator according to another aspect of the present invention is characterized by the provision of: a timing recovery device; an antenna for receiving a radio signal; frequency converting means for frequency converting said radio signal received by said antenna to a base band signal; A/D converting means for sampling said base band signal converted by said frequency converting means at a rate twice higher than a symbol rate through the use of said recovered sample clock for conversion to a digital base band signal for application to said timing recovery device; and data decision means for extracting Nyquist point data from said digital base band signal through the use of a recovered symbol clock output from said timing recovery device, for making a decision on said extracted Nyquist point data and for outputting said decided Nyquist point data as demodulated data.
A demodulator according to another aspect of the present invention is characterized by the provision of: a timing recovery device; an antenna for receiving a radio signal; frequency converting means for frequency converting said radio signal received by said antenna to a base band signal; A/D converting means for sampling the base band signal converted by said frequency converting means at a rate twice higher than a symbol rate through the use of said asynchronous sample clock for conversion to a digital base band signal for application to said timing recovery device; data interpolating means for interpolating said digital base band signal sampled by the asynchronous sample clock output from said timing recovery device, and for outputting the interpolated data as an interpolated base band signal; and data decision means for extracting a Nyquist point of the interpolated digital base band signal output from said data interpolating means based on said timing phase difference, for making a decision on said extracted Nyquist point data and for outputting the decided Nyquist point data as demodulated data.
A demodulator according to another aspect of the present invention is characterized by the provision of: a timing recovery device; an antenna for receiving a radio signal; frequency converting means for frequency converting the radio signal received by said antenna to a base band signal; A/D converting means for sampling the base band signal converted by said frequency converting means at a rate twice higher than a symbol rate through the use of an asynchronous sample clock for conversion to a digital base band signal for application to said timing recovery device; data interpolating means for interpolating said digital base band signal sampled by the asynchronous sample clock output from the timing recovery device, and for outputting the interpolated data as an interpolated base band signal; and data decision means for extracting a Nyquist point of the interpolated digital base band signal output from said data interpolating means based on both of said initial timing phase difference and said timing phase difference for phase following use, for making a decision on said extracted Nyquist point data and for outputting the decided Nyquist point data as demodulated data.